1. Field of the Invention
The present invention concerns a shrouded nozzle arrangement wherein a Low Observable Shrouded Exit Nozzle (LOSEN) is used to minimise the infra-red and radar signatures of a gas turbine engine exhaust.
2. Description of Related Art
Electromagnetic radiation, emitted or reflected by the gas turbine exit nozzle contributes significantly to the “signature” of a vehicle. By mounting the exit nozzle within a suitably shaped shroud this signature is reduced. Radar signals are absorbed or diffused by the shroud and infra-red emissions are masked, either by the shroud itself or by cool air ducted by the shroud to pass around the nozzle and the exhaust stream issuing from it. Such an arrangement, by its nature, defines a constraining envelope within which the nozzle must lie in order to be effective. This imposes constraints upon the use of reheat or thrust vectoring of the engine exhaust stream.
In a plane perpendicular to the engine centre line, the cross-sectional area of the shroud exit aperture is the same or only slightly larger than the exhaust stream in the same plane. As a consequence, the use of a thrust vectoring nozzle to direct the exhaust stream away from the engine centre line would inevitably cause hot exhaust gas to impinge upon the LOSEN shroud imposing impractical loads and temperatures. Similarly, a significant increase in exhaust gas temperature, caused by the use of reheat, would require significant cooling of the LOSEN shroud, imposing unacceptable performance penalties upon the engine.